1. Field of the Invention
The present invention relates to a power semiconductor device performing a switching of current, and in particular, to a power semiconductor device having an insulated gate structure.
2. Description of the Related Art
In general, a generated voltage (on-state voltage) in an on-state is expected to be enough small to eliminate a loss and so on in a power semiconductor device performing a current switching. To attain this object, a method in which a channel density is increased by forming a gate electrode pitch small can be adopted in a power semiconductor device having an insulated gate such as an IGBT (insulated gate bipolar transistor), a MOSFET, and so on.
In general, a mask alignment accuracy is necessary to be enhanced to form the gate electrode pitch to be small. Inparticular, a required alignment accuracy on a contact surface between a semiconductor region being a path of a current to be switched and an emitter electrode region (of an IGBT), further increases in accordance with a smallness and narrowness of the gate electrode forming small. Consequently, a difficulty in fabrication process increases. It is conceivable that an insulating film is formed in advance so as to surround only all of the gate electrodes, and then a surface of the semiconductor region is made to be the contact surface with the emitter electrode region, to make the gate electrode forming pitch small without increasing the difficulty in fabrication process as stated above. According to this method, the emitter electrode region can be formed easily so as to avoid a contact with the gate electrode, and it becomes possible to make the required alignment accuracy in forming the contact surface between the semiconductor region and the emitter electrode region unnecessary in principle.
However, in either case, when the channel density is increased, an excessive current flows at the time of a load short circuit, and a problem as a semiconductor device may be easy to occur such that the semiconductor device may be broken before, for example, a protection circuit works even if it is provided. Incidentally, there is a semiconductor device to be a reference disclosed in the following Patent Document 1, though a structure and a manufacturing method are different from the semiconductor device to be provided by the present application.
[Patent Document 1] JP-A 2001-15743 (KOKAI)